1. Field of the Invention
The present invention relates to a circuit for driving an invertor-type SRM(Switched Reluctance Motor) and, more particularly to SRM drive circuit configured such that only a single DC voltage source can be used in applying each of gate control signals for driving first and second switches of the invertor to each gate of the switching elements, for simplifying the construction of the drive circuit and reducing manufacturing costs.
2. Description of the Prior Art
Generally, a DC voltage source is required to drive switching elements constituting an invertor in SRM drive circuit. More specifically, 3-phases switched reluctance motor requires 3 DC voltage sources for driving 3 first(or upper) switching elements, respectively, and one DC voltage source for driving another 3 second(or lower) switching elements.
FIG. 1 shows a conventional SRM drive circuit diagram, and FIG. 2 shows a schematic construction of the conventional SRM. As shown in FIG. 1, the circuit is formed of A-, B-, and C-phase coils 100 to 102, and a first to sixth elements(substantially Field Effect Transistor FET elements) 103 to 108 for sequentially applying DC voltage V.sub.DC to the A-, B-, and C- phase coils 100 to 102, respectively, wherein the elements 103 and 106, 104 and 107, and 105 and 108 are coupled to both ends of the respective coils 100, 101, 102 in series, respectively. Capacitor 99, which serves to charge the residual component in the A-, B-, and C-phase coils 100 to 102 when the first to sixth FET elements 103 to 108 are turned off, is coupled in parallel with the circuitry including the above-mentioned circuit elements of FETs 103 to 108 and coils 100 to 102.
Also, first to sixth diodes 111 to 116, each being used to pass the residual component in the A-, B-, and C-phase coils 100, 101, 102, when the first to sixth FET elements 103 to 108 are turned off, towards the capacitor 99, are coupled in parallel with the first to sixth FET elements 103 to 108, respectively.
And, the A-phase coil 100 comprises the windings on the stator poles +A and -A; the B-phase coil 101 comprises the windings on the stator poles +B and -B; and the C-phase coil 102 comprises the windings on the stator poles +C and -C.
For the purpose of explaining, the circuit operation associated with A-phase will be discussed. With the first and fourth FET elements 103, 106 commonly turned on, a DC voltage V.sub.DC is applied to A-phase coil 100. Thus, poles +A and -A of the stator 120 on which A-phase coil is wound are magnetized. The magnetization of the stator poles +A and -A produces a force which attracts the pole of the rotor 121, which thus allows the rotor 121 to be rotated.
In such a manner, if the voltage V.sub.DC is sequentially applied to A-phase coil 100, B-phase coil 101, and then C-phase coil 102 through the control of the first to sixth FET elements 103 to 108 in the above-mentioned order, the continuous rotation of the rotor 121 can be maintained.
Meanwhile, when the first to sixth FET elements 103 to 108 which has applied the DC voltage V.sub.DC to each of phase coils 100 to 102 become turned off, the residual back e.m.fs at each phase coils 100 to 102 are fed to capacitor 99 through each diodes 111 to 116.
However, since ground points for the first FET elements 103, 104, 105 are different from those for the second FET elements 106, 107, 108, the voltages V1, V2, V3 for driving bases of the first FET elements 103, 104, 105 have to be not identical to the voltage V4 for driving bases of the second FET elements 106, 107, 108.
This requires 3 separate DC voltage sources for supplying voltages V1, V2, V3 for driving the first FET elements 103, 104, 105, and another one DC voltage source for supplying voltage V4 for driving the second FET elements 106, 107, 108, which causes the circuitry to be complicated, and it increases in costs for manufacturing desired circuitry.